ECRIT J. Winterbottom Internet-Draft M. Thomson Intended status: BCP Andrew Corporation Expires: September 9, 2010 March 8, 2010 Specifying Holes in LoST Service Boundaries draft-ietf-ecrit-specifying-holes-02 Abstract This document describes how holes can be specified in geodetic service boundaries. One means of implementing a search solution in a service database, such as one might provide with a LoST server, is described. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on September 9, 2010. Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents Winterbottom & Thomson Expires September 9, 2010 [Page 1] Internet-Draft Service Boundary Holes March 2010 carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Specifying Holes . . . . . . . . . . . . . . . . . . . . . . . 5 4. GML Polygons . . . . . . . . . . . . . . . . . . . . . . . . . 8 5. Holes in GML Polygons . . . . . . . . . . . . . . . . . . . . 9 6. Service Boundary Specification and Selection Algorithm . . . . 10 7. Security Considerations . . . . . . . . . . . . . . . . . . . 13 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 10.1. Normative References . . . . . . . . . . . . . . . . . . 16 10.2. Informative References . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17 Winterbottom & Thomson Expires September 9, 2010 [Page 2] Internet-Draft Service Boundary Holes March 2010 1. Introduction The LoST protocol [RFC5222] describes a protocol that's primary purpose is to map service and locations to destination addresses. LoST does this by provisioning boundary maps or areas against service URNs. The boundary is a polygon made up of sets of geodetic coordinates specifying an enclosed area. In some circumstances an area enclosed by a polygon, also known as an exterior polygon, may contain exception areas, or holes, that for the same service must yield a different destination to that described by the larger area. This document describes how holes SHOULD be specified in service boundaries defined using a GML encoding for the polygons and their internal elements (holes). GML polygons are based on elements defined in [ISO-19107]. o--------------o / \ / /\ \ / + +-----+ \ o | Hole \ o | | 1 / | | +-------+ |<--- Primary Polygon | +-------+ | | / Hole | | o \ 2 | o \ +-----+ + / \ \/ / \ / o--------------o Figure 1: Holes in a Polygon Winterbottom & Thomson Expires September 9, 2010 [Page 3] Internet-Draft Service Boundary Holes March 2010 2. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. Winterbottom & Thomson Expires September 9, 2010 [Page 4] Internet-Draft Service Boundary Holes March 2010 3. Specifying Holes Holes related to an exterior boundary polygon MUST adhere to the following rules: Rule 1: Two holes MUST NOT have more than one point of intersection. If two or more holes share a common set of boundaries then to the primary polygon these represent a single hole in the service. The internal elements (holes) should have common boundaries removed and a single hole created irrespective of whether the excluded area is itself made up of multiple service boundaries. o--------------o o--------------o / \ / \ / /\ \ / /\ \ / + +-----+ \ / + +-----+ \ o | Hole \ o o | \ o | | 1 \ | | | One \ | | +-+-------+ | =========> | +-+ Hole + | | / Hole | | | / | | o \ 2 | o o \ | o \ +-----+ + / \ +-----+ + / \ \/ / \ \/ / \ / \ / o--------------o o--------------o Incorrect Correct Figure 2: Incorrect Hole Specification with Boundary Sharing Rule 2: A hole MUST NOT have more than one point of intersection with the outer-boundary of the primary (exterior) polygon. If more than one point of intersection occurs the primary polygon is either doesn't have a hole, it has an inlet as in Figure 3, or the primary polygon SHOULD be expressed as two polygons as in Figure 4. Winterbottom & Thomson Expires September 9, 2010 [Page 5] Internet-Draft Service Boundary Holes March 2010 +------- Inlet | v o---+-----+----o o---o o----o / |%%%%%| \ / | | \ / /%%%%%%| \ / / | \ / +%%%%%%%| \ / o o \ o |%%%%%%%%\ o o | \ o | |%%%%%%%%%\ | | | \ | | +-+%%%%%%%%+ | ========> | o-o o | | /%%%%%%%%| | | / | | o \%%%%%%%%| o o \ | o \ +-----+ + / \ o-----o o / \ \/ / \ \/ / \ / \ / o--------------o o--------------o Incorrect Correct Figure 3: Correct Specification of an Inlet A--q-----------B A-q q----------B / | | \ / | | \ / | | \ / | | \ / z r-----s \ / P z r-----s P \ H | \ C H o | \ o C | | One \ | | l | \ l | | y-x Hole t | ========> | y y-x t y | | / | | | g / | g | G \ | D G o \ | o D \ / v---u / \ n / v---u n / \ \ / / \ 1 \ / 2 / \ \ / / \ \ / / F-----w--------E F-----w w--------E 1 Polgon with a 2 Polygons that map Dividing Hole to the same service Figure 4: Correct Specification of Hole with Multiple Outer-Boundary Intersections Similarly, a polygon containing a hole with an island must be represented as two polygons mapping to the same service. Winterbottom & Thomson Expires September 9, 2010 [Page 6] Internet-Draft Service Boundary Holes March 2010 Rule 3: A hole MUST be a legal polygon in accordance with the geoshape specification [geoshape]. There is no restriction on the number of points that may be used to express the perimeter of the hole. Winterbottom & Thomson Expires September 9, 2010 [Page 7] Internet-Draft Service Boundary Holes March 2010 4. GML Polygons The GML encoding of a polygon defines a enclosed exterior boundary, with the first and last points of boundary being the same. Consider the example in Figure 5. B--------------C / \ / \ / \ A D \ / \ / \ / F--------------E 43.311 -73.422 43.111 -73.322 43.111 -73.222 43.311 -73.122 43.411 -73.222 43.411 -73.322 43.311 -73.422 Figure 5: Hexagon and Associated GML Note that polygon vertices in Figure 5 are expressed using elements for clarity. The vertices can also be expressed using a element. Winterbottom & Thomson Expires September 9, 2010 [Page 8] Internet-Draft Service Boundary Holes March 2010 5. Holes in GML Polygons A hole is specified in the polygon by defining an interior boundary. The points defining the internal boundary define the area represented by the hole in the primary (exterior) polygon. The shaded area in Figure 6 is represented by the 4 points of the interior boundary specified by (w,z,y,x). F-------------E / \ / w-------------x \ / |/////////////| \ A |/////////////| D \ |/////////////| / \ z-------------y / \ / B-------------C 43.311 -73.422 43.111 -73.322 43.111 -73.222 43.311 -73.122 43.511 -73.222 43.511 -73.322 43.311 -73.422 43.411 -73.322 43.411 -73.222 43.211 -73.222 43.211 -73.322 43.411 -73.322 Figure 6: Hexagon with Hole Interior parts are specified in clockwise direction, such that the upward normal is opposite to the upward normal of the exterior part. Winterbottom & Thomson Expires September 9, 2010 [Page 9] Internet-Draft Service Boundary Holes March 2010 6. Service Boundary Specification and Selection Algorithm A service boundary is represented by a polygon that may have many vertices. The enclosed area of the polygon represents the area in which a service, expressed as a service URN, maps to a single URI. Figure 6 is used to illustrate two service boundaries. The first service boundary A->F shall be referred to as area-A, and the second service boundary w->z shall be referred to as area-w. Furthermore, area-A is directly represented by the GML encoding provided in Figure 6. Area-w is represented as a hole in area-A by the interior boundary. Since area-w is also a service boundary, a separate polygon describing this area is also required and is shown in Figure 7 (note the reversal of the vertices). 43.411 -73.322 43.211 -73.322 43.211 -73.222 43.411 -73.222 43.411 -73.322 Figure 7: GML for Area-w If this data were in a LoST server the data mappings may look similar to the example in Figure 8. This is an example only and does not represent actual LoST server provisioning or data transfer records. The example XML will not complie. Outer Area Police urn:service:sos.police 43.311 -73.422 Winterbottom & Thomson Expires September 9, 2010 [Page 10] Internet-Draft Service Boundary Holes March 2010 43.111 -73.322 43.111 -73.222 43.311 -73.122 43.511 -73.222 43.511 -73.322 43.311 -73.422 43.411 -73.322 43.211 -73.322 43.211 -73.222 43.411 -73.222 43.411 -73.322 sip:area-A-pd@example.com xmpp:area-A-pd@example.com 000 Inner Area Police urn:service:sos.police 43.411 -73.322 43.211 -73.322 43.211 -73.222 43.411 -73.222 43.411 -73.322 sip:area-w-pd@example.com xmpp:area-w-pd@example.com 000 Winterbottom & Thomson Expires September 9, 2010 [Page 11] Internet-Draft Service Boundary Holes March 2010 Figure 8: Service Boundary Specifications It is considered likely that LoST servers will need to provide responses sufficiently quickly to allow real-time queries to be performed as part of an emergency call routing flow. It is for this reason that databases supporting native geospatial query techniques are desirable and that service boundary specifications that are easily mapped to internal data structures are preferred. Using interior boundaries makes support for this operation easy, while allowing an arbitrary number of holes in a service boundary to be specified. Each polygon is stored in the geospatial database and mapped to a service URN and destination URI. Many geospatial databases natively support polygons with interior exclusions. Without native support, interior boundaries can be stored against the polygon and can checked separately. A location falls within the area described by a polygon if it is within the exterior boundary and not within any interior boundary. Winterbottom & Thomson Expires September 9, 2010 [Page 12] Internet-Draft Service Boundary Holes March 2010 7. Security Considerations This document does not introduce any security issues. Winterbottom & Thomson Expires September 9, 2010 [Page 13] Internet-Draft Service Boundary Holes March 2010 8. IANA Considerations There are no specific IANA considerations for this document. Winterbottom & Thomson Expires September 9, 2010 [Page 14] Internet-Draft Service Boundary Holes March 2010 9. Acknowledgements Thanks to Carl Reed for input provided to the list some months back and for reviewing this document. Thanks to Michael Haberler for suggesting that such a specification is required. Thanks to Avery Penniston for review and feedback. Winterbottom & Thomson Expires September 9, 2010 [Page 15] Internet-Draft Service Boundary Holes March 2010 10. References 10.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC5222] Hardie, T., Newton, A., Schulzrinne, H., and H. Tschofenig, "LoST: A Location-to-Service Translation Protocol", RFC 5222, August 2008. [geoshape] Thomson, M. and C. Reed, "GML 3.1.1 PIDF-LO Shape Application Schema for use by the Internet Engineering Task Force (IETF)", Candidate OpenGIS Implementation Specification 06-142r1, Version: 1.0, April 2007. 10.2. Informative References [I-D.ietf-ecrit-lost-sync] Schulzrinne, H. and H. Tschofenig, "Synchronizing Location-to-Service Translation (LoST) Protocol based Service Boundaries and Mapping Elements", draft-ietf-ecrit-lost-sync-09 (work in progress), March 2010. [ISO-19107] ISO, "Geographic information - Spatial Schema", ISO Standard 19107, First Edition, 5 2003. Winterbottom & Thomson Expires September 9, 2010 [Page 16] Internet-Draft Service Boundary Holes March 2010 Authors' Addresses James Winterbottom Andrew Corporation Andrew Building (39) Wollongong University Campus Northfields Avenue Wollongong, NSW 2522 AU Email: james.winterbottom@andrew.com Martin Thomson Andrew Corporation Andrew Building (39) Wollongong University Campus Northfields Avenue Wollongong, NSW 2522 AU Email: martin.thomson@andrew.com Winterbottom & Thomson Expires September 9, 2010 [Page 17]